Subversion Repositories m65c02

////////////////////////////////////////////////////////////////////////////////

//

//  Copyright 2013 by Michael A. Morris, dba M. A. Morris & Associates

//

//  All rights reserved. The source code contained herein is publicly released

//  under the terms and conditions of the GNU Lesser Public License. No part of

//  this source code may be reproduced or transmitted in any form or by any

//  means, electronic or mechanical, including photocopying, recording, or any

//  information storage and retrieval system in violation of the license under

//  which the source code is released.

//

//  The source code contained herein is free; it may be redistributed and/or

//  modified in accordance with the terms of the GNU Lesser General Public

//  License as published by the Free Software Foundation; either version 2.1 of

//  the GNU Lesser General Public License, or any later version.

//

//  The source code contained herein is freely released WITHOUT ANY WARRANTY;

//  without even the implied warranty of MERCHANTABILITY or FITNESS FOR A

//  PARTICULAR PURPOSE. (Refer to the GNU Lesser General Public License for

//  more details.)

//

//  A copy of the GNU Lesser General Public License should have been received

//  along with the source code contained herein; if not, a copy can be obtained

//  by writing to:

//

//  Free Software Foundation, Inc.

//  51 Franklin Street, Fifth Floor

//  Boston, MA  02110-1301 USA

//

//  Further, no use of this source code is permitted in any form or means

//  without inclusion of this banner prominently in any derived works.

//

//  Michael A. Morris

//  Huntsville, AL

//

////////////////////////////////////////////////////////////////////////////////

`timescale 1ns / 1ps

////////////////////////////////////////////////////////////////////////////////

// Company:         M. A. Morris & Associates 

// Engineer:        Michael A. Morris 

// 

// Create Date:     20:32:33 06/15/2013 

// Design Name:     M65C02 - WDC W65C02 Microprocessor Re-Implementation 

// Module Name:     M65C02_ClkGen 

// Project Name:    C:\XProjects\ISE10.1i\M65C02

// Target Devices:  RAM-based FPGAs: XC3S50A-xVQ100; XC3S200A-xVQ100

// Tool versions:   Xilinx ISE 10.1i SP3

// 

// Description: 

//

//  This module combines an Architecture Wizard IP instatiation of a DCM_SP to 

//  generate a 4x clock from an external crystal oscillator. It also generates

//  a reset signal to external logic, and a reset signal for internal logic and

//  the DCM. An external reset input is accepted, but buffered using a synchro-

//  nizer.

//  

// Dependencies: ClkGen.xaw

//

// Revision:

//

//  0.01    13F15   MAM     Creation Date

//

//  1.00    13F21   MAM     Corrected error in the reset generation logic. An

//                          AND reduction operator was applied to external reset

//                          shift register. An OR reduction is necessary, and

//                          is not applied. Asserting the external reset now

//                          generates a reset pulse several clock cycles in

//                          width to the internal logic. Added Clk_UART as an

//                          output taken from the Clk2X output of DCM. Clk_UART

//                          can noew be fixed at 2x ClkIn.

//

//  1.01    13H17   MAM     Adapted for use with the M65C02

//

// Additional Comments: 

//

////////////////////////////////////////////////////////////////////////////////

module M65C02_ClkGen(

    input   nRst,                       // External Reset Input (active low)

    input   ClkIn,                      // Reference Input Clk

    output  Clk,                        // Internal Clk - (M/D) x ClkIn

    output  Clk_UART,                   // 2x ClkIn

    output  Buf_ClkIn,                  // Buffered ClkIn

    output  reg Rst                     // Internal Reset

);

////////////////////////////////////////////////////////////////////////////////

//

//  Declarations

//

wire    DCM_Locked;             // DCM Locked Status Signal

reg     [3:0] DCM_Rst;          // Stretched DCM Reset (see Table 3-6 UG331)

reg     nRst_IFD;               // Input FF for external Reset signal

reg     [3:0] xRst;             // Stretched external reset (BufClkIn)

wire    Rst_M65C02;             // Combination of DCM_Rst and xRst

reg     [3:0] Rst_Dly;          // Stretched internal reset (BufClkIn)

wire    FE_Rst_Dly;             // Falling edge of Rst_Dly (Clk)

////////////////////////////////////////////////////////////////////////////////

//

//  Implementation

//

//  Implement internal clock generator using DCM and DFS. DCM/DFS multiplies

//  external clock reference by 4.

ClkGen  ClkGen (

            .USER_RST_IN(DCM_Rst[0]),           // DCM Rst generated on FE Lock 

            .CLKIN_IN(ClkIn),                   // ClkIn          = 14.7456 MHz

            .CLKIN_IBUFG_OUT(Buf_ClkIn),        // Buffered ClkIn = 14.7456 MHz

            .CLKFX_OUT(Clk),                    // DCM ClkFX_Out  = 58.9824 MHz 

            .CLK0_OUT(),                        // Clk0_Out unused 

            .CLK2X_OUT(Clk_UART),               // Clk2x_Out (FB) = 29.4912 MHz 

            .LOCKED_OUT(DCM_Locked)             // When 1, DCM Locked 

        );

//  Detect falling edge of DCM_Locked, and generate DCM reset pulse at least 4

//  ClkIn periods wide if a falling edge is detected. (see Table 3-6 UG331)

fedet   FE1 (

            .rst(1'b0),             // No reset required for this circuit 

            .clk(Buf_ClkIn),        // Buffered DCM input Clock

            .din(DCM_Locked),       // DCM Locked signal

            .pls(FE_DCM_Locked)     // Falling Edge of DCM_Locked signal

        );

always @(posedge Buf_ClkIn or posedge FE_DCM_Locked)

begin

    if(FE_DCM_Locked)

        DCM_Rst <= #1 4'b1111;

    else

        DCM_Rst <= #1 {1'b0, DCM_Rst[3:1]};

end

//  Synchronize asynchronous external reset, nRst, to internal clock and

//      stretch (extend) by 16 clock cycles after external reset deasserted

//

//  With Spartan 3A(N) FPGA family use synchronous reset for reset operations

//  per synthesis recommendations. so only these FFs will use asynchronous

//  reset, and the remainder of the design will use synchronous reset.

always @(posedge Buf_ClkIn or negedge DCM_Locked)

begin

    if(~DCM_Locked)

        nRst_IFD <= #1 0;

    else

        nRst_IFD <= #1 nRst;

end

always @(posedge Buf_ClkIn or negedge DCM_Locked)

begin

    if(~DCM_Locked)

        xRst <= #1 ~0;

    else

        xRst <= #1 {~nRst_IFD, xRst[2:1]};

end

assign Rst_M65C02 = ((|{~nRst_IFD, xRst}) | ~DCM_Locked);

always @(posedge Buf_ClkIn or posedge Rst_M65C02)

begin

    if (Rst_M65C02)

        Rst_Dly <= #1 ~0;

    else

        Rst_Dly <= #1 {1'b0, Rst_Dly[3:1]};

end

//  synchronize Rst to DCM/DFS output clock (if DCM Locked)

fedet   FE2 (

            .rst(Rst_M65C02),

            .clk(Clk),              // System Clock

            .din(|Rst_Dly),         // System Reset Delay

            .pls(FE_Rst_Dly)        // Falling Edge of Rst_Dly

        );

always @(posedge Clk or posedge Rst_M65C02)

begin

    if(Rst_M65C02)

        Rst <= #1 1;

    else if(FE_Rst_Dly)

        Rst <= #1 0;

end

endmodule